1. Field of the Invention
The present invention relates to an image forming apparatus, and more particularly, to an image forming apparatus such as an inkjet printer or the like, which forms an image on a recording medium by discharging ink onto the recording medium.
2. Description of the Related Art
An inkjet printer forms an image on recording paper by driving a recording head in accordance with image forming data, and causing ink to be discharged from nozzles of the recording head. The ink discharge device in a recording head includes devices based on a piezo actuator method, wherein the vibration plate of a pressure chamber is caused to deform by means of a piezoelectric element (piezo element), thereby applying pressure to the pressure chamber and hence causing ink to be discharged from the nozzle of the pressure chamber.
In an inkjet printer using a laminated type piezoelectric element, if a voltage is applied to a piezoelectric element during ink discharge, the piezoelectric element extends in the direction of lamination, but as a result of this movement, not only does the volume of the pressure chamber increase or decrease, but there is also a risk that the entire pressure chamber will move upward or downward, and if this latter effect is too great, then there is a risk that sufficient ink discharge capacity will not be obtainable. In order to prevent this, a composition is adopted wherein the side of the of the piezoelectric element opposite to the side where the vibration plate applies pressure to same, and the side walls of the pressure chamber, are fixed by means of a restricting member, thereby causing the pressure chamber to perform expanding and contracting deformation in a highly efficient manner. However, since the discharge performance will not be stable if the restricting member is not registered accurately in position, then manufacturing costs are required in order to implement this.
On the other hand, technology is known wherein, when drive energy is supplied to the piezoelectric element of a nozzle for discharging ink, a drive energy of a level which does not cause ink to be discharged is applied to the piezoelectric element of a nozzle that is not to discharge ink, thereby preventing the introduction of bubbles into the pressure chamber of a nozzle that is not to discharge ink (see Japanese Patent Application Publication No. 11-157076).
However, although the inkjet printer in Japanese Patent Application Publication No. 11-157076 is able to prevent the introduction of air bubbles into pressure chambers that are not to discharge ink, it does not necessarily do away with the need for the aforementioned restricting member.